1. Field of the Invention
The present invention relates to a technology for supplying toner in an image forming apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus in which a toner image is formed by using a two-component developer, toner is consumed by repeatedly performing an image formation. Therefore, a consumed amount of toner needs to be supplied successively to a developing unit. Typically, toner is stored in a toner container such as a toner cartridge and a toner bottle to be supplied to the developing unit. When the toner container becomes empty, the toner container is replaced by a new one.
Some toner supplying devices employ a powder pump for supplying the toner into the developing unit. Meanwhile, a toner end sensor needs to be provided to the toner supplying device for detecting a toner end. For example, a light transmission sensor is arranged at a vertical portion of a nozzle of the toner supplying device and detects whether the toner container has become empty.
If the image forming apparatus is always operated at normal temperature and normal humidity, the toner can be supplied appropriately. However, under a high temperature and high humidity condition, fluidity of the toner is lowered, which may cause toner blocking or other adverse phenomena inside the toner container. In the toner supplying device employing the powder pump, a toner consumption amount in the developer is estimated by fixing a time period per single driving of the powder pump. In a system having only one toner-supplying time period table, the time period per single driving of the powder pump is short, so that the pressure generated by the powder pump is relatively low. Thus, the toner blocking that has occurred inside the toner container is difficult to remove. The toner blocking causes insufficient supplying of toner, error in detecting the toner end, and the like. The error in detecting the toner end indicates that the toner container is detected to have become empty although the toner still remains therein.
To overcome the drawback mentioned earlier, the applicants have proposed a technology disclosed in Japanese Patent Application Laid-open No. 2007-148277, in which if it is detected that toner does not exist in the toner container, a time period per single driving of a powder pump is increased. With such technology, the toner blocking that has occurred inside the powder container can be removed.
In a toner supplying mechanism that includes a supplying pump, the developing unit and the supplying pump are connected by a conveying path such as a tube. Toner is supplied into the developing unit from the toner container by switching on and off the supplying pump. However, a pressure inside the supplying path is in some cases lowered due to a time interval from a previous toner supply. Due to this, a difference occurs between an actual toner supplying amount and a cumulative toner supplying amount that is calculated. In this case, the toner supplying amount can be increased by increasing the time period per single driving of the supplying pump in the similar manner to the technology mentioned earlier. Although a time period required for the toner end can be delayed, the toner supplying amount cannot be accurately determined. Thus, detection accuracy of the toner near end decreases.